Permeability tuning system



June 22, 1943. c. WENTWORTH 2,322,722

PERMEABILITY TUNING SYSTEM Filed May 29, 1942 1N VEN TOR. CHANOL mWENTWORTII.

Patented June 22, 1943 PERMEABILITY TUNING SYSTEM Chandler Wentworth,Haddon Heights, N. J., assignor to Radio Corporation of America, acorporation of Delaware Application May 29, 1942, Serial No. 444,974

9 Claims. (Cl. 171-242) The present invention relates to permeabilitytuning systems and more particularly to adjustable magnetically tunedresonant circuits which are capable of operating more efiiciently andover a wider range of frequencies than known similarly-tuned circuits.

One of the objects of the invention is to so construct and arrange thecoil that it will tune the circuit of which it is a part over anextended range of frequencies.

Another object is to provide a low loss (high Q) tuned circuit forobtaining higher gain and greater selectivity per amplifier stage thanhitherto obtained with conventional circuits.

Another object is to provide a coil system particularly adaptable forhigh frequency uses.

A still further object of the invention is to increase the tuning rangeobtainable at high frequencies with a given ferro-magnetic core.

The novel features characteristic of my invention are set forth withparticularity in the appended claims. The invention itself, however,both as to its organization and mode of operation together with furtherobjects and advantages thereof will best be understood by reference tothe following description taken in connection with the accompanyingdrawing where in Fig. 1 shows a preferred form of coil arrangement inaccordance with the invention; Fig. 2 shows a modified form of theinvention; and Fig. 3 shows the coil system of the invention serving asthe input coupling means to an amplifier stage.

The tuning range of a given core at any frequency depends upon the coreand coil geometry and the current distribution over the surface of thecoil. With a given core the tuning range increases (1) as the coillength increases up to the length of the core; (2) as the couplingbetween the core and coil is increased; (3) as the winding density isincreased; and (4) as the current distribution approaches atheoretically uniform current sheet over the surface of the coil.

The winding-density increase in tuning range is really due to animprovement in current distribution, because to effect the increase intuning range the winding density must be increased by reducing the wiresize and spacing between turns and not by adding a second layer to thecoil, hence providing a more uniform current distribution.

At high frequencies the inductances involved are small; this means shortcoils with wide spacing between turns. Both of these conditions tend todecrease the tuning range. Some improvement can be obtained byincreasing the length of coil at the expense of winding density, butunder these conditions the current distribution over the coil surface isvery poorthe current is concentrated in narrow channels widely spaced,whereas it should be uniformly distributed over the entire surface.

If a coil is wound having twice as many turns as is desired itsinductance will be four times too high, If four of the coils are woundand connected in parallel the resulting inductance will be the desiredinductance. If all four of these coils are placed end to end andconnected in por allel such that their mutual inductances are allaiding, the result is, in eifect, a long coil with the desiredinductance and a fairly good current distribution. A further improvementin current distribution can be made by making a quadrifilar winding. Ofcourse, a winding consisting of as many strands as desired could bemadethe more strands the better the current distribution. The strands,of course, must be uniformly and closely spaced in a single layer overthe surface of the coil form for best results.

With conventional coils it is practically impossible to provide ironcore tunin at high and ultra-high frequencies with any reasonable range.As indicated above, at such high frequencies the coils are required tobe very short or the spacing between turns becomes unreasonably largeand only very limited range is possible. I have found that by using aplurality of coils which are short with respect to their diameter and byconnecting them in parallel, the tuning range even at ultra-highfrequencies may be extended as much as approximately 15%,

In Fig. 1 I have shown a plurality of short coils A, B and C, threehaving been shown by way of example, placed end to end on a coil formand electrically connected in parallel with their magnetic flux mutuallyaiding. The adjustable tuning core F may be of the type which consistsof finely divided or comminuted magnetic material, such as iron dust,held together with a suitable insulating binder.

In order to show the effect of connecting coils in parallel thefollowing measurements were made with different coil combinations. Eachcoil was 1 inches long, of No. 20 single enamel copper Wire wound onstyrol tubing having inch outside diameter and inch internal diameter:

The capacity was held constant for the nocore and the core-all-way-inconditions. The core was inserted in the coil and the frequency waschanged to bring the coil to resonance again.

From the above data it can be seen that a tuning range approximately 15%greater can be obtained by using coils in parallel to make effectively alonger coil. In some cases the Q is improved.

Another form of coil that may be used is shown in Fig. 2, wherein theseveral coils A, B and C are wound together and in parallel on a commonform, which for the sake of clarity is not shown. Except for the pointof connection at their ends the several coils are insulated from oneanother.

In Fig. 3 a pair of coil systems P and S, each of which may be of theform shown in Fig. 1 or in Fig. 2, serves as the coupling means betweena source of signals and the input of an amplifier T. The source ofsignals may be an antenna circuit or the output of a precedingamplifier.

While I have shown and described certain pre ferred embodiments of myinvention, it will be understood that modifications and changes may bemade without departing from the spirit and scope of the invention, aswill be understood by those skilled in the art.

What I claim is:

1. An inductance device comprising a plurality of coils disposed end toend and e1ectri-' cally connected in parallel, and a magnetic corearranged for axial movement with respect to said coils.

2. An inductance device comprising a plurality of coils disposed end toend and electrically connected in parallel with their magnetic fluxmutually aiding, and a comminuted magnetic core arranged for axialmovement with respect to said coils.

3. An inductance device comprising a plurality of coils wound on a formand disposed end to end, said coils being electrically connected inparallel with their magnetic flux mutually aiding, and a comminutedmagnetic core adapted to be moved axially within the coil form.

4. An inductance device comprising a plurality of short coils disposedend to end and electrically connected in parallel, a coil form on whichthe several coils are wound, and a magnetic core adapted to be movedaxially within the coil form.

5. An inductance device comprising a plurality of short coils disposedend to end and electrically connected in parallel with their magneticflux mutually aiding, a coil form on which the several coils are wound,and a comminuted magnetic core adapted to be moved axially Within thecoil form,

6. An inductance device comprising a coil having a plurality of windingswhich are wound together on a form, the turns of said windings beingspaced and only the terminals of the windings being electricallyconnected to eiTect a parallel connection of the windings with theirmagnetic flux mutually aiding, and a comminuted magnetic core arrangedfor movement within the coil form.

7. An adjustable magnetically tuned resonant circuit, comprising aplurality of coils electrically connected in parallel and with theirmagnetic flux mutually aiding, and an adjustable magnetic corecooperating with said coils, the arrangement being such that theoperating range of said circuit i extended beyond that obtainable with asingle coil having substantially the same inductance as the plurality ofparallel coils.

8. An adjustable magnetically tuned resonant circuit, comprising aplurality of coils co-axially disposed end to end, electricallyconnected in parallel and with their magnetic flux mutually aiding, andan adjustable magnetic core cooperating with said coils, the arrangementbeing such that the operating range of said circuit is extended beyondthat obtainable with a single coil having substantially the sameinductance as the plurality of parallel coils.

9. An adjustable magnetically tuned resonant circuit, comprising a coilhaving a plurality of windings only the terminals of which areelectrically connected to connect the several windings in parallel withtheir magnetic flux mutually aiding, and an adjustable magnetic corecooperating with said windings, the arrangement being such that theoperating range of said circuit is extended beyond that obtainable witha single coil winding having substantially the same inductanoe as theplurality of parallel coil windings.

CHANDLER WENTWORTI-I.

DISCLAIMER 2,322,722.-Oha-ndler Wentworth, Haddon Heights, N. J.PERMEABILITY TUNING SYSTEM. Patent dated June 22, 1943. Disclaimer filedDec. 13, 1945, by assignee, Radio Corporation of America. Hereby entersthis disclaimer to claims 1 to 9 inclusive of said Letters Patent.

[Oficial Gazette January 29, 1946.]

DISCLAIMER 2,322,722.Oha'ndler Wentworth, Haddbn Heights, N. J.PERMEABILITY TUNING SYSTEM. Patent dated June 22, 1943. Disclaimer filedDec. 13, 1945, by assignee, Radio Corporation of America. Hereby entersthis disclaimer to claims 1 to 9 inclusive of said Letters Patent.

[Oflicial Gazette January 29, 1946.]

